VIENNA, Feb 28 (Reuters) - Austria will freeze the bank accounts of 18 Ukrainians following a request from Ukraine's foreign ministry and pending possible European Union sanctions, the foreign ministry said on Friday.

"Austria has decided to freeze possible bank accounts and assets of 18 Ukrainian citizens in Austria. This has been done on the basis of an official request by the Ukrainian foreign ministry," the ministry said.

It called the move "a temporary precautionary measure until EU restrictive measures enter into force".

After Ukraine suffered its bloodiest day since the Soviet era last week, the 28-nation EU agreed in principle to impose sanctions such as visa bans and asset freezes on unnamed senior Ukrainian officials.

Austria said it would freeze accounts via a central bank decree under its foreign currency law. It did not identify the people affected or say how much wealth was seized.

"The decree from the National Bank provides the appropriate legal basis to be able to determine which assets are actually in Austria and to prevent potential abuse," Foreign Minister Sebastian Kurz told the Austria Press Agency.

The EU cannot unilaterally tell banks to freeze assets without a legal decision agreed among all member states.

Ukraine's acting prosecutor general said on Wednesday the country will ask international organisations to help trace bank accounts and assets controlled by ousted President Viktor Yanukovich and his allies.

Austria's FMA markets watchdog has already warned banks to be vigilant about dealing with customers from Ukraine.